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“Think Green, Drive Yellow!” the ethanol ads cajole, but as we illustrated in last May’s Alternative-Fuels treatise (“2020 Foresight”), its lower-energy content means that, unless E85’s pump price is 25-30 percent less than gasoline’s, you’re spending more to get where you’re going. To date, neither modern farming techniques nor congressional pork has succeeded in delivering corn-likker at that magic price point. But modern biochemistry appears to have noodled a way to make pure ethanol from cornstalks, wood chips, water bottles, old tires, switchgrass — any carbon-rich detritus.

At January’s North American International Auto Show, GM announced a partnership with biology-based renewable energy firm Coskata Inc., which in turn unveiled plans to open a demonstration facility later this year that will produce 40,000 gallons of pure ethanol at an estimated cost of $1/gallon, using less than a gallon of water per gallon of ethanol — big breakthroughs both. A 100-million-gallon/year facility is scheduled to be up and running by 2011.

How does Coskata brew its cheap hooch? Like other stalks-‘n’-stems-to-alcohol schemes you may have heard of, it enlists specialist microorganisms to do the heavy lifting, but instead of assigning them the task of breaking down starches and complex carbohydrates into a sugary mash for the still, these specialist bugs breathe in carbon-monoxide and hydrogen and sweat out ethanol. The stalks or tires are first heated to 1800-plus degrees F, but not burned. This breaks the compounds down into CO, H2 and other junk removed by a scrubber. This pure syngas (the CO/H2 blend that many towns once used to illuminate their gas streetlamps) then gets pumped into the bioreactor — a plastic tube full of water and thin tubes made of a Gore-Tex-like material through which the syngas diffuses, feeding the bacteria lining the tubes.

Coskata hasn’t tinkered with the bacteria’s genetics, rather it’s bred these microorganisms like race horses, selecting a master race that produces only ethanol (actually, in nature they produce ethnoic acid, but part of Coskata’s patented bioreactor process stops their digestion at ethanol). Other bacterial strains Coskata is breeding produce butanol and propanol. In nature, these elite microbes might have colonized underwater thermal vents or swine-farm lagoons. They’re completely safe (anaerobes die in the presence of oxygen), they don’t need light, and they reproduce naturally so the bioreactor can run for months without a “clean-out.”

A key bioreformer advantage over some catalytic syngas-to-ethanol systems is that the latter produces multiple products from which ethanol must be separated, adding cost. The vaporized low-proof ethanol/water gas then passes through thin tubes made of a special hydrophilic (loves water) coating that grabs the steam, condenses and recycles it, leaving a 99.7-percent-pure stream of ethanol coming out the other end.

A secret to this system’s low cost is energy management. Once the super-heating process gets up to temperature, it sustains itself on the energy released breaking all those chemical bonds. That heat must be extracted before the syngas hits the microbes, and it can power electric turbines or serve some other purpose like drying pulp in a paper mill where waste wood materials feed the reactor. Even the ethanol separation tubes require half the energy a typical distillation stack would consume. Per Argonne National Lab’s well-to-pump studies, the resulting ethanol contains 7.7 times the energy consumed in its production.

Because practically any carbon-rich feedstock can be used, ethanol plants can be built almost anywhere, creating jobs, reducing the energy wasted in transporting feedstocks and hedging our energy supply against localized natural disasters. It promises 84-percent-lower greenhouse gas emissions than gasoline. And it’ll make driving cheaper. I’ll drink to that.